Means for controlling hydraulically operated working cylinders



Sept. 10, 1940. J Q A 2,214,308

MEANS FOR CONTROLLING HYDRAULICALLY OPERATED wonxme CYLINDERS Filed Nov.15, 1938 a Sheets-Shed z a A9 I 1414 a m l3 L I J. POLAK 2,214,308

MEANS FOR'CONTROLLI NG HYDRAULICALLY OPERATED WORKING CYLINDERS Sept.10, 1940.

Filed Nov. 15, 1938 3 Sheets-Sheet 3 Ihv n-lzw Patented Sept. 10, 1940UNITED STATES MEANS FOR CONTROLLING HYDRAULI- CALLY OPERATED WORKINGCYLIN- DERS Josef Polak, Prague, Czechoslovakia Application November 15,1938, Serial No. 240,582 In Czechoslovakia November 16, 1937 3 Claims.

For obtaining a high mould closing power in hydraulically operateddie-casting and like machines it has already been proposed to employ apressure intensifier which many times increases the pressure in theclosing cylinder shortly before the casting operation. Up to thisincrease this pressure has corresponded to that of the hydraulicaccumulator operating the machine. The operative sequence of thepressure intensifier and of the press cylinder are controlled jointly bya controlled slide valve, the piston of which during its axial motionfirst uncovers successively control passages which convey the waterunder pressure to the pressure intensifier, in order to place theclosing cylinder under the increased pressure referred to, and thereuponuncovers passages which conduct the water under pressure to the presscylinder for bringing about the casting operation. The motion of theslide valve must proceed very rapidly, in order that the controlpassages may be also rapidly uncovered, as otherwise (should thepassages be opened sluggishly) high losses due to throttling will occur,resulting in the motions in the con- 25 trolled working cylinderproceeding not with the required suddenness, but with a slowlyincreasing speed, which is undesirable.

The period which elapses between the opening of the passages for thepressure intensifier and of those for the press cylinder shallhereinafter be referred to as the advance interval. In view of therequired very rapid motion of the slide valve and of the short distanceavailable it is very short. During the advance interval the pressure inthe pressure intensifier must have reached its full height, in orderthat at the start of the casting operation the mould shall be heldclosed with the necessary force. For this a definite period of time isnecessary, which in very many cases is longer than the advance intervalreferred to above, so that the requisite increase in pressure in theclosing cylinder will not yet have been reached, when the force producedby the casting operation (the metal injected into the mould) seeks toopen the mould. It has hitherto been sought to meet this difficulty byeither retarding the motion of the slide valve or increasing thedistance of the controlled passages leading to the intensifier or thepress cylinder. The former expedient is combined with greater lossesthrough throttling and a retardation in the operative motions, whilstsuch limits are set to the latter expedient through the dimensionspossible in carrying it into practice that the purpose aimed at cannotbe realised.

To overcome these disadvantages is the object of the present inventionwhich is best described with reference to the accompanying drawings, inwhich is illustrated a constructional example of a die-casting machineinstallation for carrying the method under discussion into effect.

Figure 1 shows diagrammatically the entire arrangement,

Figures 2, 3 and 4 show the controlled slide valve with the passagescontrolled by it to an 10 enlarged scale and in difierent positions,

Figure 5 shows a modified form of the slide valve and Figure 6 a sectionon line (1-1) of Figure 5.

A is the closing cylinder, B1 the cylinder in u communication with it ofthe pressure intensifier, B2 the intensifier piston, 01 the presscylinder, C2 the press piston, D the control apparatus of knownconstruction, used for controlling the closing cylinder and containing anon-return 20 valve l, E the control apparatus used for actuating theslide valve and comprising two valves of known construction and F thecasing for the slide valve. I

Into the space H of the closing cylinder A 25 pressure liquid isintroduced by actuating the control apparatus D. The space J of theclosing cylinder A is under the constant pressure of the accumulator.The piston G is thus capable of bringing the half K of the mould, whichis fixed to it, against the immovable part L of the mould. l

The piston Q of the slide valve is of greater cross-sectional area thaneach of the two seatin'g surfaces of the piston 0. When the space N isfilled with pressure liquid, the piston 0 is forced against its lowerseating A11, whereby the admission of water under pressure through Pfrom the accumulator is shut 01! (Figures 1 and 2).

The auxiliary control apparatus E is connected by its passages with thepassages of the casing F for the slide valve and with the hydraulicsystem of the machine. By depressing the foot lever M the valve 2 israised and the valve 3 is pressed down on its seating by the water underpressure. The space N in the casing F is thereby connected by way of thepassage S and the pipe A9 with the outflow and the pistons O and Q ofthe slide valve will move in the direction of the arrow shown in Figures1 to 5 under the pressure of the water entering at P under pressure.

The motion of the slide valve can continue with undiminished velocityuntil the edge R of the u piston Q closes the e 8. when the piston Q hasreached this position (Figure 3), the edge T of the niston hascompletely uncovered the passage U, through which and the pipe Vconnected to it liquid under pressure is conveyed unhindered 'to thepressure intensifier 131. Before the edge T commences to uncover thepassage U, the edge A4 of the piston 0 will have moved beyond thepassage As and closed it, so that the connection of the latter by way ofthe space Am with the passage Ac which communicates with the outflow isinterrupted.

In the space H of the closing cylinder A a high pressure is thusproduced through the action of the intensifier, which pressure produces,the mould closing force required for the casting operation. During thecontinued motion of the slide valve pressure liquid can escape out ofthe space N only by way of the passages W1 and W2 and the adjustablethrottle valve X, as through the pipe A: no water can flow out by way ofthe closed valve 3 of the auxiliary control apparatus E. The piston O ofthe slide valve can therefore move only at a velocity determined by theadjusted opening at X. This velocity remains constant until the edge Yof the piston Q again uncovers the passage S, the edge T of the piston 0not having yet reached the edge Z of the passage A2. As soon as the edgeY of the piston Q uncovers the passage S, the liquid can again flowunhindered out of the space N above the'slide valve through the boresmin the piston Q and the annular space As, the passage S and the pipeA9. The piston 0 therefore again moves under the pressure of thepressure water with an undiminished velocity, until its rests on itsupper seating A12 (Figure 4), the edge T having uncovered the passage A2and the pressure water entering the press cylinder C for carrying outthe casting operation.

Thus, to sum up, the essence of the controlling method consists in this,that the slide valve moves at first rapidly, then slowly in anadjustable manner and finally rapidly again. The duration of theadjustable slow motion of the slide valve is that period of time, bywhich the pressure water has to enter into the press cylinderappropriately later than into the pressure intensifier.

On the foot lever M at the auxiliary control apparatus E rising, thespace N above the slide valve receives pressure water through the pipeA3, which acts on the piston Q of the slide valve and forces the pistonwith full velocity on to its lower seating A11 (Figures 1 and 2). Bythis means however the supply of pressure water into the press cylinderand the pressure intensifier is shut off, and their communication withthe outflow passage As by way of the pipe A14, the passages A1, A5 andthe annular space A or by way of the pipe V, the annular space A13, thepassages A2, A1, A5 and-the annular space A10 is established.

It will be obvious, that instead of the pressure intensifier cylinderand the press cylinder used in the constructional example describedabove for die-casting machines other working cylinders can be controlledin accordance with the present controlling method, the hydraulicallyoperated pistons of which are to be moved in such a manner that theirmovements are interdependent with respect to time.

In die-casting and like machines the press piston together with themasses taking part in its motion has imparted to it on the way from itsposition of rest, until itimpinges onthe material to be pressed, fromwhich moment only it can impart its pressure-exerting action on thelatter, a high velocity and a consequent kinetic energy which manifestsitself at the moment, at which the pressing pressure commences to act,as a highly undesirable increase in the speciflc'pressure in thematerial being pressed. In many cases this results in the mould opening.In order to overcome this disadvantage the press piston is at firstbrought up to the material to be pressed as slowly as possible (startingmotion'of the press piston) and is from this moment onwards caused toperform its actual operative motion which proceeds under high workingpressure and at a-velocity adapted to the requirements.

Figure 5 shows a constructional form of the slide valve, which enablesthe press piston to be given the slow starting motion just referred to.For this purpose the piston O has in its lower controlling part a grooveA forming a passage of relatively small cross-section. In that positionof the slide valve, in which the admission of pressure water into thepressure intensifier can already take place (Figure 3), the pressurewater will therefore flow into the press cylinder C1 through the passagegroove A15 as well, although greatly throttled in this passage, by wayof the passage A2, the passage A1 and the pipe A14 and will move thepress piston C2 with less force and a slower starting velocity. Thiscontinues, until the slide valve has reached the position shown inFigure 4 or the piston O of the slide valve has uncovered the passage A2for allowing the pressure water to flow through unhindered.

What is claimed is:

1. In die casting and like machines, intensifier and press cylindersincluding fluid operated pistons adapted to move in predetermined timedsequence, a valve device having first and second outlets connectedrespectively with the intensifier and press cylinders and having aninlet, said valve device including a sliding piston actuated by thefluid entering said inlet to successively uncover the outlets connectedwith the intensifier and press cylinders, means for retarding themovement of the sliding piston following the opening of the first outletand prior to the opening of the second outlet, the movement of thesliding piston before and after retardation being substantiallyunimpeded and relatively rapid, and a device for controlling saidsliding piston.

2. A die casting machine as claimed in claim 1 characterized in thatsaid retarding means includes adjustable throttling means cooperatingwith a part of the sliding piston, said part of the piston having apassage therein whereby fluid may by-pass said throttling means.

3. A die casting machine as claimed in claim 1 characterized by theprovision of a passage in the sliding piston for passing a quantity offluid to effect a slow starting motion of the press cylinder piston.

JosriF PoLAK.

